ON THE SOURCE OF MUSCULAR POWER. 25" 



formed into muscular work ; and secondly, that the food does not re- 

 quire to become organized tissue before its metamorphosis can be ren- 

 dered available for muscular power; its digestion and assimulation in- 

 to the circulating fluid — the blood — being all that is necessary for 

 this purpose. It is, however, by no means the non-nitrogenous por- 

 tions of food alone that are capable of being so employed, the nitro- 

 genous also, inasmuch as they are combustible, and consequently ca- 

 pable of furnishing actual energy, might be expected to be available 

 for the same purpose, and such an expectation is confirmed by the 

 experiments of Savoy upon rats,* in which it is proved that these 

 animals can live for weeks in good health upon food consisting almost 

 exclusively of muscular fibre. Even supposing these rats to have 

 performed no external work, nearly the whole of their internal mus- 

 cular work must have had its source in the actual energy developed 

 hy the oxidation of their strictly nitrogenous food. 



It can scarcely be doubted, however, that the chief use of the ni- 

 trogenous constituents of food is for the renewal of muscular tissue ; 

 the latter, like every other part of the body, requiring a continuous 

 change of substance, whilst the chief function of the non-nitrogenous 

 is to furnish by their oxidation the actual energy »vhich is in part 

 transmuted into muscular force. 



The combustible food and oxygen coexist in the blood which cour- 

 ses through the muscle, but when the muscle is at rest there is no 

 chemical action between them. A command is sent from the brain 

 to the muscle, the nervous agent determines oxidation. The poten- 

 tial energy becomes active energy, one portion assuming the form of 

 motion, another appearing as heat. Here is the source oj animal 

 heat, here the origin of muscular poioer ! Like the piston and cylin- 

 der of a steam-engine, the muscle itself is only a machine for the 

 transformation of heat into motion ; both are subject to wear and 

 tear and require renewal, but neither contributes in any important de- 

 gree by its own oxidation to the actual production of the mechanical 

 power which it exerts. 



From this point of view it is interesting to examine the various 

 articles of food in common use, as to their capabilities for the pro- 

 duction of muscular power. The writer therefore made careful esti- 

 mations of the calorific value of different materials used as food, by 



* ' Tue Lancet; 186S, pages 3S1 and 412. 



